In the past few years, computer viruses have caused damage to computer systems throughout the world. A computer virus is a program capable of operation on a computer system, such as a personal computer, that is self-replicating and that can “infect” other programs by modifying them or their environment such that a call to an infected program results in an action that the user may not like.
Computer systems today typically run operating systems having user accounts for users of the systems. A user logs into the computer system under a user account and has authority to add, edit, delete or use most of the resources available in the computer system. Additionally, applications running in the user's account have the same authority as the user. This arrangement presents a computer virus with a doorway to most of the resources in the computer system. For instance, if an application is infected by a virus, the virus is able to spread to any resource that the application may access including other files located on the computer system. Conventional virus detection software is often unable to stop the spread of viruses, as exemplified by periodic outbreaks of computer virus infections.